Allow receiving broadcast packets in UDP

[jackpot51]

This allows the reception of UDP broadcast packets. They will fall through to the process_udp function. The tcp and icmp functions also receive potential broadcast packets, but they should already be discarded.

[dlrobertson]

The destination address is not checked to see if it is the broadcast address before sending ICMP error responses currently (RFC 1122 § 3.2.2). Currently this conditional is the only thing keeping us from causing a broadcast storm due to a weird broadcast packet. The specific panic is here, and is due to the packet created for the no_icmp_to_broadcast test having no payload.

[whitequark]

@dlrobertson Wow, your tests already paid off. Thanks a lot!

[jackpot51]

@whitequark, I believe @dlrobertson is working on a fix, to prevent the ICMP error message from being sent

[dlrobertson]

After a rebase, tests should pass here.

[whitequark]

@jackpot51 Can you rebase?

[jackpot51]

Yep, will do

[jackpot51]

@whitequark it is done

[whitequark]

Any chance you can write a test for this?

[jackpot51]

Sure!

[jackpot51]

@whitequark I do not see any current tests for UDP in the ethernet interface, am I mistaken?

[dlrobertson]

@jackpot51 https://github.com/m-labs/smoltcp/blob/master/src/iface/ethernet.rs#L828-L911 is an example of a test in the ethernet interface for UDP. Essentially you could do the same thing as the second half of that test, but add a socket to the socket set that is listening to the port of interest.

[jackpot51]

Ok, cool

[whitequark]

@jackpot51 ping?

[whitequark]

Needs tests

[jackpot51]

Sorry @whitequark, I have been busy porting cargo.

[dlrobertson]

I added tests with redox-os/smoltcp#1

[jackpot51]

@whitequark the tests from @dlrobertson are now merged